The invention relates generally to x-ray tubes and, more particularly, to a magnetic coupler drive for transmitting torque to the rotating anode of the x-ray tube.
X-ray systems typically include an x-ray tube, a detector, and a bearing assembly to support the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then emits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in a computed tomography (CT) package scanner.
X-ray tubes include a rotating anode structure for the purpose of distributing the heat generated at a focal spot. An x-ray tube cathode provides a focused electron beam that is accelerated across a cathode-to-anode vacuum gap and produces x-rays upon impact with the anode. Because of the high temperatures generated when the electron beam strikes the target, it is necessary to rotate the anode assembly at high rotational speed.
The anode is typically rotated by an induction motor having a cylindrical iron-copper or copper rotor built into a cantilevered axle that supports a disc-shaped anode target and an iron stator structure with copper windings that surrounds an elongated neck of the x-ray tube. Specifically, the rotor resides inside the x-ray tube and is attached to the bearing/anode shaft, with the stator assembly residing outside the x-ray tube in either air or oil for cooling thereof. In operation, the stator functions to generate a magnetic field between the stator and the rotor by having a high current passed through a plurality of windings included therein. The high current passing through the stator windings generates the magnetic field, thereby transmitting torque from the stator to the rotor according to known DC motor principles.
The rotor-stator arrangement of typical x-ray tubes, with the rotor residing inside the x-ray tube and the stator assembly residing outside the x-ray tube, presents limits on the motor efficiency and performance that can be achieved. For example, the large rotor-stator gap resulting from placement of the rotor inside the x-ray tube vacuum and the stator assembly outside the x-ray tube vacuum significantly reduces motor efficiency. Additionally, the rotor-stator arrangement requires cooling mechanisms for cooling the stator windings due to the large currents (e.g., 5-17 amps) needed therein to overcome motor inefficiency.
Therefore, it would be desirable to have a method and apparatus for driving the rotating anode with improved efficiency. It would further be desirable for such an apparatus to operate at a lower temperature, require less input power, and occupy less space outside the x-ray tube housing.